1. Field of the Invention
The present invention relates to a method of rubbing an alignment layer of a liquid crystal display device capable of solving a problem that the alignment layer is not normally rubbed due to interference between a pattern spacer formed on a substrate and a rubbing cloth in a rubbing process.
2. Discussion of the Related Art
The present invention relates to a rubbing method, and more particularly to a rubbing method capable of minimizing interference between a pattern spacer formed on a substrate and a rubbing cloth in a rubbing process.
Further, the present invention relates to a rubbing method, and more particularly to a method of fabricating a liquid crystal display device using the rubbing method and a liquid crystal display device formed thereby. An object of the present invention is to provide a liquid crystal display device capable of improving display quality by reducing a disclination region generated by height difference of the pattern spacer and a method of fabricating the same.
As an information-oriented society has been developed, various flat panel display devices are widely used instead of conventional cathode ray tube (CRT) to display visual information.
The flat panel display devices include a plasma display panel (PDP), a field emission display device (FED), a liquid crystal display device (LCD), an organic light emitting diode (OLED) and the like. Among those flat panel display devices, the LCD, which is widely used in various fields such as display screens of a mobile phone and a computer monitor and a display screen of a large-sized TV, is the most representative flat panel display device.
The liquid crystal display device produces an image using liquid crystal molecules having an intermediate property between a liquid phase having fluidity and a solid phase having a crystal state.
That is, the LCD produces a desired image by varying an alignment direction of the liquid crystal molecules according to the electric field to adjust light transmittance using anisotropy of the liquid crystal molecules in which an optical property and a dielectric constant are different according to minor and major axes.
Hereinafter, a conventional liquid crystal display device will be described in detail.
The conventional liquid crystal display device includes a liquid crystal panel formed of two substrates facing each other and bonded to each other while a liquid crystal layer is interposed therebetween.
The two substrates may include, for example, a color filter substrate and a thin film transistor substrate. A distance between the two substrates is maintained by a pattern spacer.
In a case shown in FIG. 1A, the pattern spacer is formed on the color filter substrate.
As shown in FIG. 1A, a substrate 100 includes a black matrix 110 arranged in a matrix on the substrate 100 to define pixel regions and color filters 120 formed on the pixel regions.
The pattern spacer is spaced from a neighboring pattern spacer of the black matrix by a specific distance.
The black matrix serves to prevent light from being transmitted through a region excluding the pixel regions in which the liquid crystal is normally operated. The black matrix may be formed of metal such as chromium or a double film of a chromium/chromium oxide film. Also, the black matrix may be formed of polymeric resin.
The pattern spacer may be formed of, for example, negative photoresist. As shown in FIG. 1B, the pattern spacer is formed in a circular, octagonal, or square shape.
Meanwhile, the liquid crystal molecules should be aligned in a predetermined direction to normally operate the liquid crystal interposed between the two substrates.
For this, after alignment layers are formed on the two substrates, a rubbing process is performed on the alignment layers to align the liquid crystal molecules.
FIG. 2 illustrates a rubbing process.
As shown in FIG. 2, a rubbing roll 310 wrapped with a rubbing cloth 330 is rotated around a central shaft 320. While the rubbing roll moves toward a substrate having an alignment layer (not shown), fibers 340 implanted into the rubbing cloth are in contact with the alignment layer to perform a rubbing process.
That is, the fibers of the rubbing cloth form microgrooves in the alignment layer. Side chains extended from a polymeric main chain forming the alignment layer are arranged in one direction along the microgrooves. The liquid crystal molecules are arranged in one direction along the side chains of the alignment layer.
Further, the substrate may move toward the rubbing roll without movement of the rubbing roll. The rubbing roll and the substrate may move simultaneously to perform a rubbing process.
However, during the rubbing process, the patterns having height difference formed on the substrate physically interfere with the fibers of the rubbing cloth. The physical interference causes difficulty when the alignment layer aligns the liquid crystal molecules.
When there is physical interference between the rubbing cloth and the various patterns, the alignment layer is not sufficiently rubbed, thereby reducing an alignment capability of the alignment layer which aligns the liquid crystal molecules. Accordingly, a disclination region, in which the liquid crystal is not normally operated, increases to reduce a contrast ratio.
FIGS. 3A to 3C are photographs obtained by observing a color filter substrate using a polarization microscope after a liquid crystal panel including a color filter substrate and a thin film transistor array substrate is completed and divided.
As shown in FIGS. 3A to 3C, in a region where the rubbing process is normally performed, the liquid crystal molecules are normally aligned to maintain a full black state. On the other hand, in a region where the rubbing process is not normally performed, the liquid crystal molecules may be not normally aligned as indicated by circles.
The region where the rubbing process is not normally performed seems to be brighter than other regions on the black screen due to a light leakage phenomenon.
Particularly, among various patterns having height difference, the pattern spacer for maintaining a cell gap between two substrates is relatively higher than other patterns. Accordingly, the interference between the pattern spacer and the rubbing cloth becomes a main factor which reduces an alignment capability of the alignment layer.